self doubt

Question

Consider the following Regular expression:

1. (a+b)*abb(a+b)*
2. (a+b)*a(a+b)*bb(a+b)*
3. (a+b)*ab(a+b)*b(a+b)*
4. (a+b)*abb(a+b)*a

 

Which of the above regular expression are equivalent ?

Answer 1

1 and 2

Comments

Why not 3 ?

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option 3 we can generate abab string but option 1 and 2 not

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Is there any efficient way to check the equivalency of language ?

plz explain  .............